Working Man's Burbon

[LockDoc]

Originally Posted by HO455

I have about 200 miles on the new engine and all is well with it (No leaks yet!). It has much better off idle torque than the old 305. One thing that has become apparent is there is a much more pronounced vibration at highway speeds than before. When we were dropping the new engine in I discovered that one of the motor mounts had been cross threaded when it was last installed. (I couldn't have checked it before hand, that would've been smart so I did it the hard way, with lots of cursing to make it easier.). So my thinking is the new motor mounts made the engine sit higher in front and may have put the drive shaft angles out of spec.
First thing was to put the rear end on jack stands and set the rear ride height. (I had cut down a 2x4 when I when to the alignment shop to check all four corners for height before they aligned it.). Using this board to set the height I squirmed under the truck with my trusty angle finder. The first angle to check is the transmission. I prefer to measure the angle off of the end of the u-joint cap. But the one at the transmission is the spring clip style which I would rather not have to remove. Fortunately the transmission yolk is machined pretty well and I am fairly happy with it being true to the output shaft centerline. (You can verify the surface by reading the angle finder on the bottom and then rotate the shaft and get the reading with it on the top. They should be the same if the surface is true.). Measure the angle of the first drive shaft, the second shaft and then the pinon angle of the rear end. The photos show the finder hanging by the magnet. I didn't use the magnet when taking the readings . I use the V-block side as it is a more positive way of locating the finder. I was able to mimic the readings with the magnet side to take the pictures. I was not happy with the yolk surfaces on the rear end so I used a socket to take a reading off of the u-joint cap.
The readings ended up being 3.5* down on the transmission
0* on the front drive shaft
2* down (down at the rear) on the rear drive shaft
2* up on the pinon.
It looks like I have some work to do. The front u-joint should be in the 1 to 1.5 degree range not 3.5 degrees. I will go out in the morning and raise the rear of the transmission. I think that if I can get the tranny to 2* then the forward drive shaft will move to about the same and then most likely I will have to shim the pinon to finish the alignment. More to come.

It seems like there is always something to throw a monkey wrench in the works..... Hope you get it sorted out.

LockDoc

[HO455]

Progress was made today! But first let me correct my post from yesterday. I did not correctly post the angle directions. The correct information is:
Transmission 3.5 degrees down
Front shaft 0 degrees
Rear shaft 2 degrees UP
Pinon angle 2 degrees DOWN
I jacked the rear of the transmission up and slid a 1/2" piece of plate under the mount, lowered the transmission back down and after double checking my ride height, I took a new round of readings.
Now the transmission angle is 2 degrees and the front shaft is 1 degree. Victory at that end! The second shaft was now just shy of 2 degrees. Now with a one degree difference between the transmission and the front shaft angles, and with the pinon and the transmission at the same angle I should be good as long as the other two u-joint angles aren't too extreme This arrangement puts the u-joint operating angles at:
Front 1*
Center 3*
Rear. 4*
A one degree shim under the axle would make things perfect. But I don't think that it will be necessary. So I drilled a couple of holes in the plate and bolted it in place.
As LockDoc says there's always one more monkey wrench! I needed to replace the old tranny mount bolts with longer ones and knowing that at some point GM switched to metric fasteners on the mounts I cleaned the old bolts to make sure I got the correct fasteners. This lead to the discovery that the PO had apparently cranked metric bolts into the standard thread mount. After bolting the mount down the new 3/8 NC bolts and one came up tight and one didn't. I guess a new mount is in order. I hope it won't change the geometry, but we will see. I had to remove the metal loop strap that goes around the emergency brake cable to get a good reading on the yolk and that bolt was stripped too. My poor Burban must have been owned by a neanderthal at some point.
I got the WMB back down on the ground and went for a drive. The harsh vibration is now gone.
Today's post accompanied by Doug MacLeod.

https://m.youtube.com/watch?v=h2R8OTXJsxw